Transverse electromagnetic (TEM) system and method of manufacture

ABSTRACT

An assembly is provided for a transverse electromagnetic (TEM) system. The assembly includes a support frame and at least one resistive sheet. The support frame includes an upper plate and a lower plate. The upper plate defines a first inner surface and an opposed first outer surface. The lower plate defines a second inner surface and an opposed second outer surface. The at least one resistive sheet is coupled to at least one of the upper plate or the lower plate, and extends parallel to the upper plate and lower plate from an exterior of the support frame. The resistive sheet has an inner end disposed proximate the at least one of the upper plate or lower plate and an outer end disposed opposite the inner end, and has a variable resistance that is greater at the outer end than at the inner end.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application,Ser. No. 62/742,544, filed Oct. 8, 2018 and entitled “TransverseElectromagnetic (TEM) System and Method of Manufacture,” the entirecontent of which is hereby incorporated by reference.

BACKGROUND

Transverse electromagnetic (TEM) cells are used to measure materialproperties, two-dimensional (2D) scattering from components, andreceived signals at low radio-frequency (RF) frequencies. TEM cellstypically contain a test cavity that allows propagation of a TEM wave,wherein the reflected or received signal contains information about thecomponent being tested. However, many of these materials and componentsthat are tested have very low return signal levels. Current TEM cellshave very limited dynamic range and are not capable of reliablymeasuring these low levels. Moreover, current TEM cells may be unstableand susceptible to outside noise. As a result, providing reliable testresults is limited and/or use of existing TEM cells cannot provide allthe needed tests.

SUMMARY

Accordingly, a need exists for a more stable TEM system that canreliably measure low-level signals from test components and that is lesssusceptible to outside noise.

Some examples provide a support frame for a transverse electromagnetic(TEM) system. The support frame includes an upper plate, a lower plate,side support members, an upper support structure, and a lower supportstructure. The upper plate defines a first inner surface and an opposedfirst outer surface. The first inner surface is oriented toward a TEMtest space. The lower plate defines a second inner surface and anopposed second outer surface. The second inner surface is orientedtoward the first inner surface of the upper plate and toward the TEMtest space. The TEM test space is defined between the first innersurface of the upper plate and the second inner surface of the lowerplate. The side support members are disposed between the upper plate andthe lower plate proximate a periphery of the test space. The uppersupport structure is coupled to and supports the upper plate. The uppersupport structure extends from the first outer surface of the upperplate. The lower support structure is coupled to and supports the lowerplate. The lower support structure extends from the second outer surfaceof the lower plate.

In other examples, a method is provided (e.g., for forming a supportframe for a transverse electromagnetic (TEM) system. The method includescoupling a lower support structure to a lower plate. The lower platedefines a second inner surface and an opposed second outer surface. Thesecond inner surface is configured to be oriented toward a TEM testspace, and the lower support structure extends from the second outersurface of the lower plate. The method also includes positioning sidesupport members above the second inner surface of the lower plateproximate a periphery of the test space. Also, the method includescoupling an upper support structure to an upper plate. The upper platedefines a first inner surface and an opposed first outer surface. Theupper support structure extends from the first outer surface of theupper plate. Further, the method includes positioning the upper plateabove the side support members with the first inner surface orientedtoward the second inner surface of the lower plate and toward the TEMtest space, with the TEM test space defined between the first innersurface of the upper plate and the second inner surface of the lowerplate.

Other examples provide an assembly for a transverse electromagnetic(TEM) system. The assembly includes a support frame and at least oneresistive sheet. The support frame includes an upper plate and a lowerplate. The upper plate defines a first inner surface and an opposedfirst outer surface. The first inner surface is oriented toward a TEMtest space. The lower plate defines a second inner surface and anopposed second outer surface. The second inner surface is orientedtoward the first inner surface of the upper plate and toward the TEMtest space, with the TEM test space defined between the first innersurface of the upper plate and the second inner surface of the lowerplate. The at least one resistive sheet is coupled to at least one ofthe upper plate or the lower plate, and extends parallel to the upperplate and lower plate from an exterior of the support frame. Theresistive sheet has an inner end disposed proximate the at least one ofthe upper plate or lower plate and an outer end disposed opposite theinner end, and has a variable resistance that is greater at the outerend than at the inner end.

Still other examples provide an assembly for a transverseelectromagnetic (TEM) system. The assembly includes a support frame andresistive blocks. The support frame includes an upper plate and a lowerplate. The upper plate defines a first inner surface and an opposedfirst outer surface, with the first inner surface oriented toward a TEMtest space. The lower plate defines a second inner surface and anopposed second outer surface, with the second inner surface orientedtoward the first inner surface of the upper plate and toward the TEMtest space. The TEM test space is defined between the first innersurface of the upper plate and the second inner surface of the lowerplate. The support frame defines a length extending from a source sidetoward an object side and width extending normal to the length. Theresistive blocks are disposed along the width proximate the object side,with each resistive block having first and second resistive sidesopposed to each other and oriented along the width.

Other examples provide a method that includes providing a support framecomprising an upper plate and a lower plate. The upper plate defines afirst inner surface and an opposed first outer surface. The first innersurface is oriented toward a transverse electromagnetic (TEM) testspace. The lower plate defines a second inner surface and an opposedsecond outer surface. The second inner surface is oriented toward thefirst inner surface of the upper plate and toward the TEM test space,with the TEM test space defined between the first inner surface of theupper plate and the second inner surface of the lower plate. The methodalso includes coupling at least one resistive sheet to at least one ofthe upper plate or the lower plate. The at least one resistive sheetextends parallel to the upper plate and lower plate from an exterior ofthe support frame. The resistive sheet has an inner end disposedproximate the at least one of the upper plate or lower plate and anouter end disposed opposite the inner end, with the resistive sheethaving a variable resistance that is greater at the outer end than atthe inner end.

Other examples provide a source assembly for a transverseelectromagnetic (TEM) system. The source assembly includes a first guideand a second guide. The first guide is configured to receive a signalfrom a supply, and includes a first shell defining a first cavity. Thefirst guide is configured to extend proximate an upper plate of the TEMsystem. The second guide is configured to receive a reference signalfrom the supply. The second guide includes a second shell defining asecond cavity. The second guide is configured to extend proximate alower plate of the TEM system, and is spaced a distance from the firstguide to define a gap having a gap width. At least one of the firstguide or second guide includes an access opening configured to provideaccess to at least one of the first cavity or the second cavity.

In other examples, a method is provided that includes mounting a firstguide to a transverse electromagnetic (TEM) structure to extendproximate an upper plate of the TEM system. The first guide includes afirst shell defining a first cavity. The method also includes couplingthe first guide to a supply for receiving a signal from the supply.Also, the method includes mounting a second guide to the TEM structure adistance from the first guide to define a gap having a gap width. Thesecond guide extends proximate a lower plate of the TEM system, andincludes a second shell defining a second cavity. At least one of thefirst guide or second guide comprises an access opening configured toprovide access to at least one of the first cavity or the second cavity.The method also includes coupling the second guide to the supply forreceiving a reference signal from the supply. Further, the methodincludes transmitting the signal and reference signal via the firstguide and the second guide, respectively, toward an object, andreceiving a return signal from the object.

Still other examples provide a source assembly for a transverseelectromagnetic (TEM) system. The source assembly includes a first guideand a second guide. The first guide is configured to receive a signalfrom a supply, and is configured to extend proximate an upper plate ofthe TEM system. The second guide is configured to receive a referencesignal from the supply, and is configured to extend proximate a lowerplate of the TEM system. The second guide is spaced a distance from thefirst guide to define a gap having a gap width. The first guide has afirst tapered side and the second guide has a second tapered sideoriented toward each other. The first tapered side and the secondtapered side each include a taper that continuously reduces in slopetoward an end point oriented toward an object to be tested in the TEMsystem.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides an exploded perspective view of a support frame for aTEM system, according to an embodiment of the present disclosure.

FIG. 2 provides a plan view of the support frame of FIG. 1.

FIG. 3 provides a front sectional view of the support frame of FIG. 1taken along line 3-3 of FIG. 2.

FIG. 4 provides a side sectional view of the support frame of FIG. 1taken along line 4-4 of FIG. 2.

FIG. 5 provides a plan sectional view of the side support members ofFIG. 1 taken along line 5-5 of FIG. 3.

FIG. 6 provides a plan view of a composite plate, according to anembodiment of the present disclosure.

FIG. 7 provides a view of the composite plate of FIG. 6 that includesconductive tape disposed along seams, according to an embodiment of thepresent disclosure.

FIG. 8 provides a side sectional view of an upper plate and uppersupport structure, according to an embodiment of the present disclosure.

FIG. 9 is a flow chart illustrating a method to manufacture a supportframe for a TEM system according to an embodiment of the presentdisclosure.

FIG. 10 is a plan view of a TEM system including an assembly includingan RF absorbing structure according to an embodiment of the presentdisclosure.

FIG. 11 is a side view of upper and lower resistive sheets according toan embodiment of the present disclosure.

FIG. 12 is a plan view of a printed side of a resistive sheet accordingto an embodiment of the present disclosure.

FIG. 13a is a side view of a resistive sheet of FIG. 12 mounted to anupper plate.

FIG. 13b is a side view of a resistive sheet of FIG. 12 mounted to alower plate.

FIG. 14 is a plan view of a resistive block according to an embodimentof the present disclosure.

FIG. 15 is a side view of a resistive block according to an embodimentof the present disclosure.

FIG. 16 is a side view of the opposite side of the resistive block ofFIG. 15.

FIG. 17 is a flow chart illustrating a method to manufacture an RFabsorbing structure for a TEM system according to an embodiment of thepresent disclosure.

FIG. 18 is a side view of a source assembly in accordance with variousembodiments.

FIG. 19 is a sectional view of aspects of the source assembly of FIG.18.

FIG. 20 is a sectional view of aspects of the source assembly of FIG.18.

FIG. 21 is flow chart illustrating a method according to an embodimentof the present disclosure.

FIG. 22 is an exploded view of a TEM system according to an embodimentof the present disclosure.

FIG. 23 is a block diagram of an aircraft production and servicemethodology.

FIG. 24 is a block diagram of a manufacturing environment according toan embodiment of the present disclosure.

Corresponding reference characters indicate corresponding partsthroughout the drawings.

DETAILED DESCRIPTION

Referring to the figures, some examples of the disclosure provide atransverse electromagnetic (TEM) system, or TEM cell, capable of testingcomponents (e.g., measure material properties, two-dimensional (2D)scattering from components, and received signals at low RF frequencies).Various examples include a parallel plate waveguide to measure materialproperties of a component having very low return signals, such as todetermine electromagnetic (EM) properties of the component. For example,in a radar application, the TEM system is capable of measuring the (2D)radar cross-section (RCS) of, for example, vehicle components, as wellas antenna performance. However, it should be appreciated that theherein disclosed examples of TEM systems can be used to measuredifferent properties of different components.

The TEM system in some examples generally includes a TEM cell that hasan external frame structure (exoskeleton). In an exemplary embodiment,the TEM cell is formed from a plurality of sectional panels that, whenassembled, define an internal test space for performing testing todetermine the EM properties of an object being tested. The example TEMsystem also includes a radio frequency (RF) absorbing structure that isdisposed around an exterior of the test space defined by the TEM cell.

As described herein, the shape of the TEM cell and use of an RFabsorbing structure around the perimeter of the test cell allows formore reliable measurement of material properties of the object undertest at low RF frequencies (e.g., 30 MHz to 500 MHz). For example, theRF absorbing structure may be implemented as impedance sheets that arepositioned to surround the perimeter of the TEM cell to thereby reducereflections, particularly from the metal edge/air boundary of thefixture (e.g. reduces scattering from the TEM cell edges), whichimproves the dynamic range of the TEM system. By placing the TEM cellfixture within a shield enclosure outside RF noise is also reduced.Moreover, the mechanical design of the TEM cell, including the shape ofthe TEM cell, improves long term measurement stability and backgroundlevels.

FIG. 1 illustrates an exploded perspective view of a support frame 103formed in accordance with various embodiments. FIG. 2 provides a planview of the support frame 103, FIG. 3 provides a front sectional view ofthe support frame 103, FIG. 4 provides a side sectional view of thesupport frame 103, and FIG. 5 provides a plan sectional view of the sidesupport members 114. Generally, the support frame 103 may be used with aTEM system 100, for example for testing EM properties of an object.(See, e.g., FIG. 10 and FIG. 22 for additional discussion regarding TEMsystem 100.) As seen in FIG. 1, the support frame 103 may be understoodin various embodiments as including a first support assembly 102 (orupper support assembly), a second support assembly 104 (or lower supportassembly), and side support members 114 disposed between the firstsupport assembly 102 and the second support assembly 104. In variousembodiments, the first and second support assemblies 102 and 104 eachinclude at least a corresponding plate.

It may be noted that in various embodiments, the support frame 103 isshaped to help improve TEM system performance. For example, in theillustrated example, as best seen in FIG. 2, the depicted upper plate106 (and lower plate 110 which is similarly shaped) defines a footprint170. The footprint 170 has a length 171 that extends from a source side120 (or first end) toward an object side 122 (or second end), and awidth 172 that extends normal or perpendicular to the length 171. It maybe noted that the source side 120 may be understood as corresponding tothe end of the plate where a source is mounted, and the object side 122as corresponding to the end of the plate opposite the source side. Anobject to be tested may not be located exactly at the end of the plate,but may be positioned further inboard.

A source (e.g., signal generator/receiver 136) for waves for TEM testingmay be disposed at the source side 120, and an object 204 (see FIG. 5)to be tested disposed at the object side 122. As also seen in FIG. 5, anincident wave 200 may be sent from the source 136 to the object 204along a propagation direction 206, and a reflected wave 202 returnedfrom the object 204 toward the source 136. The footprint 170 has atapered width along the propagation direction 206 that extends at leastpartially from the source side 120 toward the object side 122. As bestseen in FIG. 5, the side members 114 are also laid out along thefootprint 170. The tapered shape helps to avoid discontinuity and tohelp ensure the test wave 200 is as close to a plane wave as practical,while allowing the area of the test space 118 to flare outwardly alongthe propagation direction 206 to minimize scattering.

With returned reference to FIG. 2, the depicted example footprint 170includes a first parallel portion 174, an intermediate tapered portion176, and a second parallel portion 178. The first parallel portion 174is located proximate the source side 120 (e.g., outside of the source136 along the length 171), and includes first sides 175 that extendparallel to each other along the length 171 of the footprint 170. Thesecond parallel portion 178 is located proximate the object side 122(e.g., outside of the object 204 along the length 171), and includessecond sides 179 that extend parallel to each other along the length171. The intermediate tapered portion 176 is interposed between thefirst parallel portion 174 and the second parallel portion 178, andincludes intermediate sides 177 that are tapered inwardly along thelength 171 along the propagation direction 206. Accordingly, the sidesof the footprint 170 are parallel in front of the source and behind theobject but tapered between the source and object, allowing for taperingalong the desired or intended path of waves along with a compact sizeoutside of the desired or intended path of waves in the TEM test space118.

For example, as best seen in FIG. 3 (which is a sectional view takenalong lines 3-3 of FIG. 2) and FIG. 4 (which is a sectional view takenalong lines 4-4 of FIG. 2), the support frame 103 includes an upperplate 106, a lower plate 110, side support members 114, the uppersupport structure 108, and the lower support structure 112. The upperplate 106 and upper support structure 108 form the first supportassembly 102, and the lower plate 110 and lower support structure 112form the second support assembly 104. The side support members 114 helpsupport the upper plate 106 and space the upper plate 106 a distancefrom the lower plate 110 to provide a volume for testing an object(e.g., testing EM properties of an object).

The depicted upper plate 106 defines a first inner surface 152 and afirst outer surface 154 that is opposed to the first inner surface 152.The first inner surface 152 is oriented toward a TEM test space 118. Forexample, an object whose EM properties are to be tested may be placed inthe TEM space 118. The lower plate 110 defines a second inner surface162 and a second outer surface 164 that is opposed to the second innersurface 162. The second inner surface 162 of the lower plate 110 isoriented toward the first inner surface 152 of the upper plate 106 andtoward the TEM test space 118. Accordingly, the TEM test space 118 isdefined between the first inner surface 152 of the upper plate 106 andthe second inner surface 162 of the lower plate 110.

The upper plate 106 and lower plate 110 generally define the top andbottom of a parallel plate waveguide (e.g., a TEM cell) that allows forthe propagation of a TEM wave. For example, an incident wave (e.g., TEMtest wave) may be generated that propagates within the parallel platewaveguide toward a test object 204 from which the wave is reflected as areflected signal. The reflected signal contains information about theobject 204 according to EM testing technology (e.g., EM properties,performance characteristics, etc.) Generally, the upper plate 106 andlower plate 110 are made of a conductive material (e.g., aluminum) toform the parallel plate waveguide. It is desirable to provide as smoothand continuous a surface as possible for such a parallel platewaveguide, and to avoid or minimize flexing of the upper plate 106 andlower plate 110, which may affect the background noise, interference,and/or the accuracy of a calibration of the TEM system. In variousembodiments, the support frame 103 may be used to define a relativelylarge TEM test space 118 (e.g., 40 feet by 60 feet). Various embodimentsdiscussed herein include upper and lower support structures 108 and 112that provide sufficient rigidity and support for the upper and lowerplates (106, 110) to allow accurate testing for such a large space. Forexample, in various embodiments, the upper and lower plates (106, 110)are formed using 1 inch thick Aluminized honeycomb core sheet, withthick face sheets. Further, various embodiments use upper and lowersupport structures as discussed herein.

In the illustrated example, and still referring to FIGS. 3 and 4, theside support members 114 are disposed between the upper plate 106 andthe lower plate 110 proximate a periphery 119 of the test space 118 (seeFIG. 1). In various embodiments, outer edges of the side support members114 are aligned with corresponding outer edges of the upper plate 106and the lower plate 110. In various embodiments, the side supportmembers 114 are formed from an electrically non-conductive material toreduce or avoid any potential interference from the side support members114. For example, in various embodiments, foam blocks may be used toprovide the side support members 114. The side support members 114support the upper plate 106 above the lower plate 110, and define theheight of the test space 118.

In various embodiments, and as shown in FIG. 5, the side support members114 include a series of blocks 114 a that are placed adjacent to eachother. Further, in various embodiments, the side support members 114define an opening 134 (e.g., a space in which no side support member 114is disposed) along the periphery 119 of the test space 118. The opening134 provides for access to the interior of the test space 118 (e.g., forplacing or removing an object to be tested). The depicted opening 134 islocated proximate the object side 122 (or side of the support frame 103in which the object 204 is placed). Locating the opening 134 proximatethe object side 122 in various embodiments helps reduce the effect ofthe opening 134 on scattering or interference during TEM testing.

It may be noted that, as discussed above, it is desirable to avoidflexing of the upper plate 106 and lower plate 110 for accurate,reliable measurements with a TEM system using the support frame 103.This is particularly so for larger support frames (e.g., test spaces 118of 60 feet×40 feet, or even larger in some embodiments). To help providesupport to the upper and lower plates (106, 110) and to help reduceflexing, while still providing a smooth continuous surface withoutinterruptions or a minimum of interruptions on the interior of the testspace, various embodiments use support structures mounted to exteriors(e.g., the portions of the plates oriented away from the test space 118)of the upper and lower plates (106, 110). For the example depicted inFIGS. 1-5, the support frame 103 includes the upper support structure108 (which forms a first support assembly 102 with the upper plate 106,and the lower support structure 112 (which forms the second supportassembly 104 with the lower plate 110).

As seen in FIGS. 1-4, the upper support structure 108 is coupled to andsupports the upper plate 106. The upper support structure 108 extendsfrom the first outer surface 154 of the upper plate 106. Accordingly,the upper support structure 108 extends up and away from the test space118, and does not intrude on the test space 118 while providing supportfor the upper plate 106, for example, to reduce any flexing by the upperplate 106. In various embodiments, the upper support structure 108includes a truss assembly 180 that includes members 181. Use of thetruss assembly 180 that extends away from the first outer surface 154helps provide rigidity and stability of the upper plate 106.

Generally, the truss assembly 180 may be understood as including members181 that run both horizontally and vertically and are attached atvarious points or nodes. It may be noted that upper beams may also bereferred to as top chords, lower beams may also be referred to as bottomchords, and interior beams may also be referred to as webs. In theillustrated example, as best seen in FIGS. 3 and 4, the members 181 ofthe truss assembly 180 include members 181 a that extend vertically,members 181 b that extend along the length of the upper supportstructure 108, members 181 c that extend across the width of the uppersupport structure, and members 181 d that extend diagonally (as bestseen in FIG. 3). The members 181, for example, may be structural shapes(e.g., square tubing, I-beams, or the like) made of 8020 steel. It maybe noted that other support structures may be utilized in variousembodiments, including other truss arrangements, or, as another example,a network of ribs or gussets that extend upward from the upper plate106.

As also seen in FIGS. 1, 3, and 4, the lower support structure 112 iscoupled to and supports the lower plate 110. The lower support structure112 extends from the second outer surface 164 of the lower plate 110.For example, the lower support structure 112 in various embodimentsincludes legs 182 that support the lower plate 110, and elevate thelower plate 110 off of the ground. Accordingly, the lower supportstructure 112 extends down and away from the test space 118, and doesnot intrude on the test space 118 while providing support for the lowerplate 110, for example, to reduce any flexing by the lower plate 110.Further, the lower support structure 112 helps elevate the test space118 off of the ground for improved isolation. In the illustratedexample, as best seen in FIGS. 3 and 4, the lower support structure 112includes members 183 that abut the lower plate 110, and from which thelegs 182 extend. The members 183 of the depicted example include members183 a that extend along the width of the lower support structure 112 andmembers 183 b that extend along the length of the lower supportstructure 112. The legs 182 and/or members 183, for example, may bestructural shapes (e.g., square tubing, I-beams, or the like) made of8020 steel. It may be noted that other arrangements of legs and/ormembers may be used in various embodiments.

It may be noted that in various embodiments, the upper plate 106 andlower plate 110 may have a relatively large area (e.g., in excess of2000 square feet). Accordingly, to provide such a large area, a numberof smaller plates may be joined to form the upper plate 106 and/or thelower plate 110. FIG. 6 provides a plan view of a composite plate 190 inaccordance with various embodiments. The composite plate 190 may be usedas an upper plate 106 and/or a lower plate 110 in various embodiments.As seen in FIG. 6, the composite plate 190 includes a plurality ofmember plates 192. For example, the member plates 192 may be abuttednext to each other to form a solid composite plate 190. The memberplates 192 in the illustrated example define seams 194 where joined toadjacent member plates 192. In various embodiments, the seams 194 may becovered (e.g., on an interior side of the member plate 192 orientedtoward an interior of the TEM test space 118) to provide a smoothsurface. The composite plate 190 depicted in FIG. 7 includes conductivetape 196 disposed along the seams 194 (the seams 194 are shown in dashedlines in FIG. 7). The use of composite plates in various embodimentsallows for use of easier to handle, acquire, and/or transport smallerindividual plates to form a larger a plate, while use of the conductivetape 196 helps to avoid or minimize any discontinuities on the face of aplate that may affect TEM performance.

While conventional mounting approaches typically use through holes inconjunction with fasteners, it may be noted that various embodiments, incontrast to conventional approaches for joining structures, utilizeblind or tapped holes. For example, FIG. 8 provides a side sectionalview of a portion of an example upper support structure 108 that ismounted to an example upper plate 106 using blind or tapped holes. Asseen in FIG. 8, a member 181 of the upper support structure 108 isjoined to the upper plate 106 using a screw 198 that is accepted by atapped hole 199. The tapped hole 199 extends into the first outersurface 154 of the upper plate 106, but not entirely through the upperplate 106. In the example illustrated in FIG. 8, the upper supportstructure 108 includes a clip 197 that is attached to the member 181,with the screw 198 passing through an opening in the clip 197 to securethe member 181 to the upper plate 106. Accordingly, the upper supportstructure 108 is joined securely to the upper plate 106 without causingany surface disruption on the first inner surface 152 of the upperplate, avoiding any resulting discontinuities from such a surfacedisruption and improving TEM performance. It may be noted that a similarmounting arrangement using tapped holes may also be used for mountingthe lower support structure 112 to the lower plate 110.

FIG. 9 provides a flowchart of a method 250 in accordance with anembodiment. The method 250 may be carried out in conjunction with orperformed using assemblies and/or processes as set forth herein. Invarious embodiments, certain steps may be omitted or added, certainsteps may be combined, certain steps may be performed simultaneously,certain steps may be performed concurrently, certain steps may be splitinto multiple steps, certain steps may be performed in a differentorder, or certain steps or series of steps may be re-performed in aniterative fashion.

At 252, an upper plate (e.g., upper plate 106), upper support structure(e.g., upper support structure 108), lower plate (e.g., lower plate110), and lower support structure (e.g., lower support structure 112)are provided. Generally, the upper plate and lower plate are configuredto define upper and lower boundaries of a TEM test space (e.g., TEM testspace 118), and the upper and lower support structures are configured toprovide support and rigidity to their corresponding plates. In someembodiments, for example, individual legs may be used to form the lowersupport structure (e.g., by joining each leg separately to the lowerplate), and a truss assembly may be utilized for the upper supportstructure. In the depicted embodiment, at 254, the lower supportstructure is formed using legs (e.g., legs 182), and, at 256, the uppersupport structure is formed with a truss assembly (e.g., by joiningmembers 181 together to form truss assembly 180).

As discussed herein, in various embodiments, the upper and lower plates(106, 110) may be composite plates. In the depicted embodiment, at 258,member plates are joined together to form each of the upper and lowerplates (106, 110) as composite plates. Further, at 260 conductive tapeis applied along seams formed between adjacent member plates. Applyingthe conductive tape along the seams (e.g., on the inner surfaces of theplates) improves the continuity of the inner surfaces, thereby improvingTEM testing performance relative to an apparatus with exposed seamspresenting surface disruptions or irregularities.

At 262, the lower support structure is coupled to the lower plate. Thelower plate defines a second inner surface and an opposed second outersurface. The second inner surface is configured to be oriented towardthe TEM test space. The lower support structure extends from the secondouter surface of the lower plate. For example, individual legs may bejoined to the second outer surface of the lower plate.

At 264, side support members (e.g., side support members 114) arepositioned above the second inner surface of the lower plate proximate aperiphery of the test space. For example, the side support members mayinclude a series of foam blocks, having a height that is the desiredheight of the test space, that are placed around the perimeter of afootprint defined by the lower plate. The blocks may be positioned to begenerally adjacent to or abutting each other around the perimeter of thelower plate or the periphery of the test space. It may be noted that thefootprint may define a tapered width as discussed herein. In variousembodiments, while most of the side support members may be adjacent orabutting each other, an opening for access to the test space may beprovided. In the illustrated embodiment, at 266, an opening (e.g.,opening 134) is provided through the side support members along theperiphery of the test space. For example, two blocks may be positionedwith a space between them, with the size of the space setting the widthof the opening. The opening may be located proximate the object side asdiscussed herein.

At 268, the upper support structure is coupled to the upper plate. Asdiscussed herein, the upper plate defines a first inner surface(configured to be oriented toward the TEM test space) and an opposedfirst outer surface (configured to be oriented away from the TEM testspace), with the upper support structure extending from the first outersurface of the upper plate. In the illustrated embodiment, the uppersupport structure is coupled to the upper plate using blind holes thatdo not extend through the upper plate. At 270, the upper supportstructure is mounted to the upper plate with screws accepted by tappedholes that extend into the first outer surface but not entirely throughthe upper plate.

At 272, the upper plate is positioned above the side support memberswith the first inner surface oriented toward the second inner surface ofthe lower plate and toward the TEM test space. The TEM test space isdefined between the first inner surface of the upper plate and thesecond inner surface of the lower plate. The TEM test space is alsocontained within an interior of a perimeter defined by the side supportmembers. With the upper plate in place, a TEM support frame isassembled. Other components (e.g., TEM test wave source/receiver,shielding components, object to be tested) may next be disposed in oraround the support frame for performance of tests.

In various embodiments, an RF absorbing structure 126 (which may includeone or more individual structures or sub-assemblies) is provided toshield an area surrounding the TEM system 100. In particular, a portionof the TEM system 100, in the exemplary embodiment, may be fabricatedusing the support frame 103 described above. Accordingly, the RFabsorbing structure 126 is utilized to reduce or eliminate EM waves thatmay be reflected outside the TEM test space 118 that is defined by thesupport frame 103. Aspects of the RF absorbing structure 126 may belocated outside of the TEM test space 118 (e.g., around a perimeter orperiphery defined by the support frame 103) and/or inside of the TEMtest space 118 (e.g., located in the object side 122 with the object 204nearer the source 136 than the absorbing structure(s).

FIG. 10 provides a plan view of the TEM system 100 including astructural assembly 1000, with the structural assembly 1000 includingthe support frame 103 (the upper plate 106 is removed in FIG. 10) andthe RF absorbing structure 126 in accordance with various embodiments.

As seen in FIG. 10, in the illustrated example, the RF absorbingstructure 126 includes a plurality of blocks 1020 that are distributedaround the perimeter of the support frame 103. It may be noted that theside support members 114 are depicted as being a generally continuousstructure for ease of illustration in FIG. 10, but, as discussed herein,may include a series of blocks.

Generally, the blocks 1020 are used to support one or more resistivesheets (or impedance sheets) such as the resistive sheets 1010 describedbelow. The resistive sheets are configured to reduce the effects ofinterference and/or scattering during TEM testing.

Resistive sheets 1010 are provided in various embodiments for the upperplate 106 and lower plate 110. FIG. 11 provides a side view of the useof resistive sheets 1010 a, 1010 b with both upper and lower plates(106, 110) in accordance with various embodiments. As seen in FIG. 11,the resistive sheets 1010 include an upper resistive sheet 1010 a thatis coupled to the upper plate 106, and a lower resistive sheet 1010 bthat is coupled to the lower plate 110. Accordingly, resistive sheets1010 a, 1010 b may be used to help smoothly dissipate current or energyfrom both the upper plate 106 and the lower plate 110.

Blocks 1020 are used to support and maintain the resistive sheets 1010a, 1010 b in their desired positions and orientations. In FIG. 11, asingle stack of blocks 1020 are shown; however, it may be noted that aseries or plurality of such blocks may be disposed around an exterior ofthe support frame 103 as shown in FIG. 10.

As seen in FIG. 11, the RF absorbing structure 126 comprises a lowerblock portion 1022, an upper block portion 1024, and an intermediateblock portion 1026. The block portions in various embodiments are madeof electrically insulating foam. The upper resistive sheet 1010 a isinterposed between the upper block portion 1024 and the intermediateblock portion 1026, and the lower resistive sheet 1010 b is interposedbetween the lower block portion 1022 and the intermediate block portion1026. The blocks are sized and configured to support and maintain theresistive sheets at the edges of the plates in accurate alignment and ata predetermined orientation (e.g., extending generally parallel from theplates).

Generally, the resistive sheets 1010 a, 1010 b are in electricalcommunication with the upper plate 106 and/or lower plate 110 andconfigured to help smoothly dissipate current from the plates. In FIG.12, the resistive sheets 1010 a, 1010 b are shown at the same elevationas the corresponding plates 106, 110 for ease of illustration; however,in various embodiments the resistive sheets 1010 a, 1010 b may be at adifferent elevation (e.g., a bottom surface of the resistive sheet 1010a, 1010 b aligned with an upper surface of the corresponding plate 106,110, or an upper surface of the resistive sheets 1010 a, 1010 b alignedwith a bottom surface of the corresponding plate 106, 110.

In various embodiments, the resistive sheets 1010 a, 1010 b extendsparallel (e.g., within 5% of parallel) to the corresponding upper orlower plate 106, 110 from an exterior of the support frame 103. Theresistive sheets 1010 a, 1010 b are supported by and maintained in adesired position by blocks 1020 disposed above and below the resistivesheets. The resistive sheets 1010 a, 1010 b have an inner end 1012 thatis disposed proximate to the corresponding upper or lower plate 106,110, and also have an outer end 1014 that is disposed opposite the innerend 1012, with the outer end 1014 at a maximum distance from thecorresponding upper or lower plate 106, 110. The resistive sheets 1010a, 1010 b have a variable resistance along a length 1011 of theresistive sheets 1010 a, 1010 b extending from the inner end 1012 to theouter end 1014. The variable resistance is greater at the outer end 1014than at the inner end 1012. The variable resistance in the illustratedembodiment varies proportionally to distance along the length 1011.Utilization of a variable resistance that is larger at the outer end1014 provides for dissipation of current or energy passing from theupper or lower plates while providing for a smooth transition inincrease in resistance, and accordingly reducing the effects ofscattering or background effects on TEM test results.

As discussed herein, the resistive sheets 1010 a and 1010 b have avariable resistance that is greater at the outer end 1014. FIG. 12provides a plan view of resistive sheet 1010 a, 1010 b in accordancewith various embodiments, FIG. 13a provides a side view of the resistivesheet 1010 a mounted to a corresponding upper plate 106, and FIG. 13bprovides a side view of the resistive sheet 1010 b mounted to acorresponding lower plate 110. The resistive sheets 1010 a, 1010 binclude a resistive side 1402 and a substrate side 1404. Generally, theresistive side 1402 includes a resistive material that has been disposedon an electrically insulating substrate. Accordingly, the printed side1402 is resistive and the substrate side 1404 is insulating.

In the illustrated example, the depicted resistive sheets 1010 a, 1010 binclude a grid 1410 of resistive portions (e.g., traces) 1412 that areconfigured to provide the variable resistance. Specifically, the grid1410 has less resistive portions 1412 proximate the inner end 1012 thanthe outer end 1014. Put another way, the grid 1410 is more resistiveproximate the outer end 1014. It may be noted that the grid 1410 of theillustrated example includes generally parallel and perpendicular traces1412 for ease of illustration; however, the traces 1412 may form othergeometric patterns to provide the variable density of printed conductivematerial and resulting variable resistance.

As seen in FIGS. 13a and 13b , for the illustrated example, theresistive side 1402 is oriented away from the corresponding upper orlower plate 106, 110 to which the resistive sheet 1010 a, 1010 b iscoupled, and the substrate side 1404 is oriented toward thecorresponding plate 106, 110. The depicted resistive sheet 1010 a, 1010b is coupled to the corresponding plate 106, 110 with conductive tape1430 (e.g., copper tape). The conductive tape 1430 is in contact withthe corresponding plate 106, 110 and the resistive side 1402 of theresistive sheet 1010 a, 1010 b, thereby electrically coupling theresistive sheet 1010 a, 1010 b to the corresponding plate 106, 110 eventhough the resistive side 1402 is oriented away from the correspondingplate 106, 110. It may be noted that other orientations (e.g., resistiveside 1402 oriented toward the corresponding plate) and/or mountings maybe utilized in other embodiments.

With returned reference to FIG. 10, as also discussed previously, thesupport frame 103 defines a length 171 that extends from the source side120 toward the object side 122, and a width 172 that extends normal orperpendicular to the length 171. The depicted RF absorbing structure 126further includes a plurality of resistive blocks 1600. As describedabove, the blocks 1020, including the resistive sheets 1010 a, 1010 b,are generally disposed along the sides of the support frame 103. In thisembodiment, the resistive blocks 1600 are generally disposed along thewidth 172 proximate the object side 122. The resistive blocks 1600 aredisposed behind the object to be tested 204 along the propagationdirection 206 as shown in FIG. 10, and help dissipate or absorb energyto reduce background effects on TEM testing. For example, the resistiveblocks 1600 may be configured to absorb EM waves that propagate to theback of the test space 118.

As seen in FIGS. 14-16, in the illustrated examples, each resistiveblock 1600 is made of an electrically insulating material, but includesresistive material disposed on a first resistive side 1602 and secondresistive side 1604. For example, the resistive block 1600 may include afoam block with R cards disposed on the first resistive side 1602 andthe second resistive side 1604. Other structures may be used in otherembodiments to provide the resistive blocks 1600. The first resistiveside 1602 and second resistive side 1604 are opposed to each other, anddisposed on opposite sides of the corresponding resistive block 1600along the width 172. The resistive blocks 1600 are disposed behind theobject 204 along the propagation direction 206 to absorb energy thatpasses the object 204 and inhibit reflection of energy. It may be notedthat when resistive blocks 1600 are used in conjunction with resistivesheets 1010 discussed herein, the resistive blocks 1600 may be placedwithin the test space 118 and be used to control a field strength fortesting, while the resistive sheets 1010 may be disposed outside of thetest space 118 and used to reduce scattering or background effects.

FIG. 14 provides a plan view of a resistive block, FIG. 15 provides aside view of the resistive block 1600 showing the first resistive side1602, and FIG. 16 provides a side view of the resistive block showingthe second resistive side 1604. The depicted resistive blocks 1600 havea front end 1620 and a rear end 1622. The front end 1620 is closer tothe source side 120 than is the rear end 1622. In various embodiments,the first resistive side 1602 and second resistive side 1604 have avariable resistance that is greater at the rear end 1622 than at thefront end 1620. Accordingly, with the front end 1620 receiving energyfrom the source 136 first, and the rear end 1622 having greaterresistance, a smooth transition from lower to higher resistance isachieved.

Various configurations of resistive material disposed on the sides ofthe resistive blocks 1600 may be utilized to provide variable resistance(e.g. resistance that varies proportionally with length from the frontend 1620 to the rear end 1622. For example, as seen in FIG. 15, thefirst resistive side 1602 (which may be formed by mounting an R card tothe side of the block 1600) includes a first geometrically taperedresistive member 1652. The first tapered resistive member 1652 istapered toward a bottom 1660 of the resistive block 1600. In theillustrated embodiment, the first tapered resistive member 1652 isformed as a triangle of resistive material having a maximum width at therear end 1622 (for highest relative resistance) tapering to an end pointat the bottom 1660 of the resistive block (for lowest relativeresistance. Further, in the illustrated embodiment, the second taperedresistive member 1654 is formed as a triangle of resistive materialhaving a maximum width at the rear end 1622 (for highest relativeresistance) tapering to an end point at the top 1662 of the resistiveblock (for lowest resistance). Accordingly, with more resistive materialat the front end 1620, the resistance is greater at the rear end 1622.Further, with first resistive side 1602 tapering toward the bottom 1660and the second resistive side tapering toward the top 1662, thedirection of tapering resistance tends to average toward the middle ofthe resistive blocks 1600, or parallel to the upper plate 106 and lowerplate 110.

In some embodiments, the resistive blocks 1600 may be separated by gaps.In the illustrated embodiment, the gaps between the resistive blocks1600 are filled by intermediate blocks 1690 that are interposed betweenthe resistive blocks 1600. For example, an intermediate block 1690 maybe interposed between pairs of neighboring resistive blocks 1600 so thatresistive blocks 1600 and intermediate blocks 1690 alternate along thewidth 172. In various embodiments, the resistive blocks 1600 may abutadjacent intermediate blocks 1690. The intermediate blocks 1690, forexample, may have a predetermined width that is selected to spaceresistive blocks 1600 from each other at a predetermined distance whilealso providing improved structural stability.

FIG. 17 provides a flowchart of a method 1700 in accordance with anembodiment. The method 1700 may be carried out in conjunction with orperformed using assemblies and/or processes as set forth herein. Invarious embodiments, certain steps may be omitted or added, certainsteps may be combined, certain steps may be performed simultaneously,certain steps may be performed concurrently, certain steps may be splitinto multiple steps, certain steps may be performed in a differentorder, or certain steps or series of steps may be re-performed in aniterative fashion.

At 1702, a support frame (e.g., support frame 103) is provided. Thesupport frame in various embodiments is assembled using one or moreaspects of the method 250 discussed in connection with FIG. 9, and/orincludes one or more aspects of the support frame 103 discussed inconnection with FIGS. 1-8. For example, the support frame includes anupper plate and lower plate spaced a distance from each other to definea TEM test space, as more fully set forth in connection with FIGS. 1-9.

At 1704, at least one resistive sheet (e.g., resistive sheet 1010) iscoupled to at least one of the upper plate or lower plate of the supportframe. In various embodiments, the resistive sheet is electrically andmechanically coupled to the corresponding upper or lower plate, andextends parallel to the corresponding upper or lower plate from anexterior of the support frame. The resistive sheet has an inner end thatis disposed proximate the corresponding upper or lower plate to which itis coupled, and an outer end opposite the inner end. The resistive sheethas a variable resistance that is greater at the outer end than theinner end.

In various embodiments, respective resistive sheets may be coupled toboth upper and lower plates (106, 110). For example, in the illustratedembodiment, at 1706, an upper resistive sheet is coupled to the upperplate, and a lower resistive sheet is coupled to the lower plate. Invarious embodiments, upper, lower, and intermediate blocks may be usedto support and/or position the resistive sheets as discussed elsewhereherein.

Various techniques may be used to provide variable resistance in variousembodiments. For example, in the illustrated embodiment, at 1708, a gridof resistive portions is provided on the resistive sheet (e.g., on aresistive side of the resistive sheet that has a substrate side andresistive side). The grid may be provided as an R card in variousembodiments. Further, in the illustrated embodiment, at 1710, theresistive side is oriented away from the corresponding upper or lowerplate, and the substrate side is oriented toward the corresponding upperor lower plate. At 1712, the resistive sheet is coupled to thecorresponding upper or lower plate with conductive tape. The conductivetape may be used to electrically couple the grid or resistive side withthe corresponding upper or lower plate.

Additionally or alternatively to resistive sheets disposed around theperiphery of a test space or support frame, in various embodimentsresistive blocks may be used in the interior of the support frame ortest space. For example, in the illustrated embodiment, at 1714,resistive blocks (e.g., resistive blocks 1600) are disposed along awidth of the of the support frame in the test space proximate an objectside of the support frame. Each resistive block has a first resistiveside and a second resistive side opposed to each other and orientedalong the width. The resistive sides, for example, may have a variableresistance that increases along the length of the correspondingresistive block in a direction away from a source of a wave for TEMtesting. The resistive sides in various embodiments may be provided as Rcards mounted to opposing sides of foam blocks.

With continued reference to FIG. 10, in various embodiments, a source136 for the TEM system 100 may be used to help determine EM propertiesof object to be tested. In the example, depicted in FIG. 10, the source136 is configured to provide an incident wave 200 toward an object 204to be tested, with a reflected wave 202 reflected from the object 204back toward the source 136. The source 136 may be used in connectionwith one or more supplies and/or processing units (not shown in FIG. 10)to receive and analyze the reflected wave 202 to determine EM propertiesof the object 204 using the TEM system 100.

The source 136 in various embodiments utilizes a pair of conductors totransmit the incident wave 200 toward the object 204. Variousembodiments discussed herein provide improved conductor pairs. Forexample, FIG. 18 provides a side view of an example source assembly thatutilizes conductor pairs. FIG. 18 provides a side view of sourceassembly 2000 that is configured to generate an incident wave (e.g.,incident wave 200) that utilizes a conductor pair including a firstguide 2010 and a second guide 2020 in accordance with variousembodiments. FIG. 19 includes a sectional view taken across lines 19-19of the first guide 2010 and second guide 2020. The source assembly 2000is coupled to a supply 2002. In the illustrated embodiment, supply 2002is configured as a data processing device and power supply unitincluding at least one processor configured to control the supply ofcurrent to the first guide 2010 and second guide 2020 to transmit theincident wave 200, as well as to utilize the reflected wave 202 todetermine EM properties of the object 204. It may be noted that thedepicted supply 2002 is shown as a single block for ease ofillustration; however, in practice the supply 2002 may be split amongmultiple physical blocks, entities, systems, or components.

In the illustrated embodiment, the first guide 2010 is configured toreceive a signal 2013 from the supply 2002. The first guide 2010includes a first shell 2012 defining a first cavity 2014. The firstguide 2010 is configured to extend proximate the upper plate (e.g.,upper plate 106) of a TEM system. For example, the first guide 2010 mayextend along an inner surface of the upper plate 106 as shown in FIG.18. The first guide 2010 is made of an electrically conductive materialand is electrically coupled to the upper plate 106.

Generally similarly, the second guide 2020 is configured to receive areference signal 2023 from the supply 2002. The second guide 2020includes a second shell 2022 that defines a second cavity 2024. Thesecond guide 2020 is configured to extend proximate the lower plate(e.g., lower plate 110) of a TEM system. For example, the second guide2020 may extend along an inner surface of the lower plate, or as anotherexample, the second guide 2020 may extend along a recess or slot of thelower plate. The second guide 2020 is made of an electrically conductivematerial and is electrically coupled to the lower plate.

As seen in FIGS. 18 and 19, the second guide 2020 is spaced a distancefrom the first guide 2010 to define a gap 2030 having a gap width 2032(corresponding to the distance). In various embodiments, at least one ofthe first guide 2010 or second guide 2020 comprises an access opening2034 that is configured to provide access to at least one of the firstcavity 2014 or the second cavity 2024. In the illustrated embodiment theaccess opening 2034 is provided through a wall of the second shell 2022proximate the supply 2002, and is schematically depicted as a hingeddoor 2035 (shown closed in FIG. 18). The access opening 2034, forexample, provides access to electrical components (e.g., cables) and/ormechanical components (e.g., aspects of an adjustment assembly asdiscussed herein) disposed within the second cavity 2024. Generally,access openings may also be used to provide access to the interior ofthe first shell 2012 and/or second shell 2022 for mounting and/oradjusting the positions of the first guide 2010 and/or second guide2020. The first guide 2010 and second guide 2020 extend generallyparallel to each other and their corresponding plates to which they aremounted. For example, in the illustrated embodiment, the first guide2010 includes a base 2011 that extends parallel to the upper plate 106,and the second guide 2020 includes a base 2021 that extends parallel tothe lower plate 110.

In various embodiments, the first and second guides 2010 and 2020 areshaped to help produce smooth transitions (e.g., changes in shape alongthe propagation direction 206) for improved TEM testing performance. Forexample, in the illustrated embodiment, as best seen in FIG. 18, thefirst guide 2010 has a first tapered side 2016 and the second guide 2020has a second tapered side 2026 oriented toward each other. The firsttapered side 2016 and second tapered side 2026 each include or define ataper 2017 that continuously reduces in slope toward an end point 2018oriented toward an object to be tested. The continuous reduction inslope allows for a smooth transition to the ends of the guides as theguides reach their ends.

In the illustrated embodiment, as shown in FIG. 19, the source assembly2000 includes a coaxial source cable 2050. Generally the coaxial sourcecable 2050 is configured to provide signals from the supply 2002 to theguides which in turn produce signals forming the incident wave 200responsive to receiving the signals from the supply 2002. The depictedcoaxial source cable 2050 includes a center conductor 2052 and an outerconductor 2054. The center conductor 2052 and outer conductor 2054 passthrough the second cavity 2024. The center conductor 2052 passes beyondthe second cavity 2024 to the first guide 2010, and is coupled to thefirst guide 2010, with the first guide 2010 receiving the signal 2013via the center conductor 2052. The outer conductor 2054 in theillustrated embodiment does not extend to the first guide 2010. Theouter conductor 2054 is coupled to the second guide 2020, with thesecond guide 2020 receiving the reference signal 2023 via the outerconductor 2054.

In various embodiments, an adjustment mechanism is provided that may beused to adjust the physical position and/or orientation of one or bothof the first guide 2010 and/or the second guide 2020, for example, tocontrol the input impedance of the source assembly 2000 by adjusting thegap width 2032 of the gap 2030. FIG. 20 provides a side sectional viewof aspects of the source assembly 2000 taken along lines 20-20. As seenin FIG. 20, the source assembly 2000 includes an adjustment assembly2040. In various embodiments, the adjustment assembly 2040 is coupled toat least one of the first guide 2010 or second guide 2020, and isconfigured to adjust a position of at least one of the first guide 2010or second guide 2020 to adjust the gap width 2032. Accordingly, theinput impedance of the source assembly 2000 may be adjusted.Alternatively or additionally, the position of the first guide 2010 withrespect to the upper plate 106 and/or the position of the second guide2020 with respect to the lower plate 110 may be adjusted. The adjustmentassembly 2040 in various embodiments may include one or more of athreaded actuator rod, gears, motor, cylinder, or linkages configured toreceive an input and, responsive to the input, adjust the position ofthe first guide 2010 and/or the second guide 2020. The input may beprovided manually (e.g., turning of the threaded actuator rod, moving ofa lever) and/or electronically (e.g., control signal to a motor).

In the illustrated example, the adjustment assembly 2040 is coupled tothe second guide 2020, and used to adjust a height of the second guide2020. For example, the second guide 2020 may be raised form an originalposition shown in solid lines to an adjusted position shown in phantomlines in FIGS. 18, 19, and 20 using the adjustment assembly 2040, toadjust the input impedance. The adjustment assembly 2040 includes a base2042 and an adjustment portion 2044. The adjustment portion 2044 iscoupled to the second guide 2020. The adjustment portion 2044 isinterposed between the base 2042 and the second guide 2020, with base2042 configured to be disposed beneath the lower plate 110. One or moreaspects of the adjustment assembly 2040 (e.g., all or apportion of theadjustment portion 2044) may be disposed within the second guide 2020,with access to those aspects provided by access opening 2034.

FIG. 21 provides a flowchart of a method 2200 in accordance with anembodiment. The method 2200 may be carried out in conjunction with orperformed using assemblies and/or processes as set forth herein. Forexample, it may be noted that the method 2200 (or aspects thereof) maybe combined with method 250 (or aspects thereof) and/or method 1700 (oraspects thereof) to provide a TEM system and/or utilize the TEM systemto test an object. In various embodiments, certain steps may be omittedor added, certain steps may be combined, certain steps may be performedsimultaneously, certain steps may be performed concurrently, certainsteps may be split into multiple steps, certain steps may be performedin a different order, or certain steps or series of steps may bere-performed in an iterative fashion.

At 2202, a first guide (e.g., first guide 2010) is mounted to a TEMstructure (e.g., support frame 103), and extends proximate an upperplate (e.g., upper plate 106) of a TEM system. The first guide includesa first shell defining a first cavity, and is electrically coupled tothe upper plate.

At 2204, a second guide (e.g., second guide 2020) is mounted to the TEMstructure at a distance from the first guide to define a gap having agap width. The second guide extends proximate a lower plate (e.g., lowerplate 110) of the TEM system. The second guide includes a second shelldefining a second cavity, and is electrically coupled to the lowerplate. At least one of the first or second guides includes an accessopening (e.g., access opening 2034) that provides access to thecorresponding first or second guide.

At 2206, the first guide is coupled to a supply for receiving a signalfrom the supply, and, at 2208, the second guide is coupled to the supplyfor receiving a reference signal from the supply.

At 2210, to couple the first and second guides to the supply, a centerconductor and outer conductor of a coaxial source cable is passedthrough the second cavity of the second guide. At 2212, the centerconductor is coupled to the first guide and the outer conductor iscoupled to the second guide. Accordingly, in the illustrated embodiment,the first guide receives a signal from the supply via the centerconductor, and the second guide receives a reference signal from thesupply via the outer conductor.

At 2214, at least one of the first or second guides is coupled to anadjustment assembly (e.g., adjustment assembly 2040). For example, theadjustment assembly may include a base and an adjustment portion, withthe adjustment portion coupled to the second guide. With the basedisposed beneath the second guide, the adjustment portion is interposedbetween the base and the second guide.

At 2216, a position of at least one of the first guide or second guideis adjusted to adjust the gap width. Accordingly, the impedance of thesource assembly including the first and second guides may be adjusted.

At 2218, the signal and reference signal are transmitted from a sourcevia the first guide and second guide, respectively. The signal andreference signal are transmitted toward an object (e.g., object 204) tobe tested, and may cooperate to form an incident wave (e.g., incidentwave 200). The incident wave is reflected off of the object, resultingin a reflected wave or return signal being transmitted back toward thefirst and second guides.

At 2220, the return signal (e.g., reflected wave 202) is received (e.g.,by a processing unit via the first and second guides). The return signalmay then be analyzed and used, at 2222, to determine EM properties ofthe object being tested.

As discussed herein, one or more of the aspects discussed above may beused in connection with a TEM system for testing an object 204. FIG. 10provides a plan view of a TEM system 100 (with the upper plate removed),and FIG. 22 provides an exploded view of aspects of the TEM system 100.As seen in FIGS. 10 and 23, the depicted TEM system 100 includes thesupport frame 103, RF absorbing structure 126, and source assembly 2000discussed herein. Various aspects of the support frame 103, RF absorbingstructure 126, or source assembly 2000 may be omitted or modified invarious embodiments. Generally, the TEM system 100 is configured invarious examples for testing the EM properties of an object. The TEMsystem 100 includes a TEM cell 101 or parallel plate waveguide definedby the support frame 103. The TEM cell 101 provides a waveguide ortransmission structure that may be utilized by the TEM system 100 fortransmitting signals.

To test an object using the TEM system 100, an incident wave 200 (e.g.,TEM test wave) is generated and propagates within the parallel platewaveguide and is reflected as a reflected signal 202 from an object 204under test. As should be appreciated, the reflected signal containsinformation about the object 204 according to EM testing technology(e.g., EM properties, performance characteristics, etc.).

It may be noted that the guides from the source assembly 2000 may beutilized in various embodiment; however, other conductors may be used inalternate embodiments. For example, in some embodiments, any conductorscapable of generating a test signal for testing the EM properties of theobject 204 (e.g., a 50 MHz to 1000 MHz EM test signal) may be utilized.In various examples, the conductors utilized to transmit the incidentwave 200 may be any type of TEM transmission line medium (e.g., two flatstrips of metal sandwiched between two parallel ground planes.

Thus, the TEM system 100 has components that define a TEM cell having aparallel plate waveguide formed in part by the upper and lower plates(106, 110) 106, 110 that are separated by a distance that defines a gapthat functions as the test space 118. It may be noted that, as discussedherein, each of the upper and lower plates (106, 110) 106, 110 in someexamples are fabricated from a plurality of sectional panels that arestructurally enhanced by the support structures 108, 112 that caninclude a plurality of I-beams or engineered shapes or extrusions, etc.that are mounted on an exterior surface of the panels that form theupper and lower plates (106, 110) 106, 110. It should be noted that invarious examples, seams between the panels are aligned to extend alongthe propagation direction 206.

In one example, the upper and lower plates (106, 110) 106, 110 alongwith the upper support structure 108 and lower support structure 112 areformed from extruded Aluminum sections, and the upper and lower plates(106, 110) 106, 110 are formed from aluminum honeycomb core panelshaving a thickness of one inch. It may be noted that in some examples,the upper and lower plates (106, 110) 106, 110 are formed as one inchaluminum honeycomb panels and have an alodined surface to preventoxidation. In one example, the maximum deflection of the upper structureunder the weight of the TEM system 100 (16,000 pounds) is approximately0.046 inches with a maximum deflection of the lower structure beingapproximately 0.018 inches.

The TEM system 100 is capable of performing one or more different testswithin the test space 118 using TEM testing techniques. For example, theTEM system 100 can perform bulk material property measurements, thinimpedance sheet measurements, 2D radar cross-section measurements, andantenna measurements, among others. In some examples, the TEM system 100performs the test(s) by operating over a frequency range of 50 MHz to 1GHz to allow implementation of time-domain gating. However, the TEMsystem 100 can operate at other frequencies as determined by a signalgenerator/receiver (e.g., source 136) coupled to the pair of shapedconductors. The signal generator/receiver can be any type of EM testsignal generation and receiving device capable of generating andmeasuring EM signals for testing the object 204. In one example, the TEMsystem 100 is excited with a tapered feed/launcher allowing for broadband operation of the TEM system 100.

In some examples, the TEM system 100 operates in the dominant mode (TE1)and propagates a transverse electromagnetic wave (electric and magneticfields perpendicular to each other and the direction of propagation),such as the incident wave 200 within the test space 118. In one example,the TEM system takes advantage of the image theory allowing for 2Dscattering and RCS measurements. It should be noted that some data fromthe measurements, such as RCS and antenna performance data are directlycollected. However, other data from the measurements, such as bulkproperties and impedance sheet data is acquired by post processing ofthe data using TEM testing algorithms.

The shape and size of the TEM system 100 can be varied. In one example,the TEM cell 100 has an overall length of 50 feet. In this example, thewidth of the source side 120 is 8 feet and the width of the object side122 is 30 feet. Accordingly, the dimensions of the TEM cell 100 may belonger and wider than known current TEM cells.

It should be noted that the thickness of the elements that form thewalls of the TEM cell can be varied to change the size of the test space118. Additionally, the dimensions of the TEM system 100 (or relativedimensions of the elements forming the TEM system 100), including theinternal and external dimensions, can be varied as desired or needed,such as based on the particular application or the object 204 to betested.

Additionally, in some examples, a shield room may be utilized thatsurrounds the TEM system 100 and is a 100 dB enclosure having dimensionsof approximately 80 feet long, 45 feet wide, and 20 feet high, with afloor weight distribution of 250 pounds/square foot.

In various examples, the TEM system 100 provides improvement in thepredicted field quality (structure and amplitude) of the testing with alarger fixture size and the addition of perimeter and verticaltreatments for RF absorbing structure. Moreover, an enlarged TEM cell ofthe TEM system 100 (compared to current TEM systems) allows anobstruction free background subtraction of a 15 foot radius region (30ns time domain gate) in some examples. Additionally, the TEM system 100has lower and much more stable noise floor levels than current TEMsystems. Thus, the TEM system 100 has improved EM and/or mechanicalproperties over current TEM cells. For example, the TEM system 100 ismore rugged, rigid, stable, and less susceptible to damage duringoperation. Additionally, the TEM system 100 has increased rigidity thatimproves background subtraction/repeatability.

Examples of the disclosure may be described in the context of anaircraft manufacturing and service method 700 as shown in FIG. 23 and anaircraft 800 as shown in FIG. 24, for example, to test one or morecomponents of the aircraft 800 during the aircraft manufacturing andservice method 700. During pre-production, illustrative method 700 caninclude specification and design 702 of the aircraft 800 and materialprocurement 704. During production, component and subassemblymanufacturing 706 and system integration 708 of the aircraft 800 takeplace. Thereafter, the aircraft 800 can go through certification anddelivery 710 to be placed in service 712. While in service by acustomer, the aircraft 800 is scheduled for routine maintenance andservice 714 (which can also include modification, reconfiguration,refurbishment, and so on).

Each of the processes of the illustrative method 700 can be performed orcarried out by a system integrator, a third party, and/or an operator(e.g., a customer). For the purposes of this description, a systemintegrator can include, without limitation, any number of aircraftmanufacturers and major-system subcontractors; a third party mayinclude, without limitation, any number of vendors, subcontractors, andsuppliers; and an operator may be an airline, leasing company, militaryentity, service organization, and so on.

As shown in FIG. 24, the aircraft 800 produced by the illustrativemethod 700 can include an airframe 802 with a plurality of high-levelsystems 804 and an interior 806. Examples of high-level systems 804include one or more of a propulsion system 808, an electrical system810, a hydraulic system 812, and an environmental system 814. Any numberof other systems can be included. Although an aerospace example isshown, the principles may be applied to other industries, such as theautomotive industry.

Apparatus and methods shown or described herein can be employed duringany one or more of the stages of the manufacturing and service method700. For example, components or subassemblies corresponding to componentand subassembly manufacturing 706 can be fabricated or manufactured in amanner similar to components or subassemblies produced while theaircraft 800 is in service. Also, one or more aspects of the apparatus,method, or combination thereof can be utilized during the productionstates 706 and 708, for example, by substantially expediting assembly ofor reducing the cost of an aircraft 800. Similarly, one or more aspectsof the apparatus or method realizations, or a combination thereof, canbe utilized, for example and without limitation, while the aircraft 800is in service, e.g., maintenance and service 714.

Thus, various embodiments include a TEM system with improved performancefor testing objects, such as components of the aircraft 800. Forexample, the RF absorbing structure allows for more reliable testing atlower RF frequencies.

As used herein, a structure, limitation, or element that is “configuredto” perform a task or operation is particularly structurally formed,constructed, or adapted in a manner corresponding to the task oroperation. For purposes of clarity and the avoidance of doubt, an objectthat is merely capable of being modified to perform the task oroperation is not “configured to” perform the task or operation as usedherein.

Any range or value given herein can be extended or altered withoutlosing the effect sought, as will be apparent to the skilled person.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

It will be understood that the benefits and advantages described abovecan relate to one embodiment or can relate to several embodiments. Theembodiments are not limited to those that solve any or all of the statedproblems or those that have any or all of the stated benefits andadvantages. It will further be understood that reference to ‘an’ itemrefers to one or more of those items.

The embodiments illustrated and described herein as well as embodimentsnot specifically described herein but within the scope of aspects of theclaims constitute exemplary means for TEM testing.

The term “comprising” is used in this specification to mean includingthe feature(s) or act(s) followed thereafter, without excluding thepresence of one or more additional features or acts.

The order of execution or performance of the operations in examples ofthe disclosure illustrated and described herein is not essential, unlessotherwise specified. That is, the operations can be performed in anyorder, unless otherwise specified, and examples of the disclosure caninclude additional or fewer operations than those disclosed herein. Forexample, it is contemplated that executing or performing a particularoperation before, contemporaneously with, or after another operation(e.g., different steps) is within the scope of aspects of thedisclosure.

When introducing elements of aspects of the disclosure or the examplesthereof, the articles “a,” “an,” “the,” and “said” are intended to meanthat there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere can be additional elements other than the listed elements. Theterm “exemplary” is intended to mean “an example of” The phrase “one ormore of the following: A, B, and C” means “at least one of A and/or atleast one of B and/or at least one of C.”

Having described aspects of the disclosure in detail, it will beapparent that modifications and variations are possible withoutdeparting from the scope of aspects of the disclosure as defined in theappended claims. As various changes could be made in the aboveconstructions, products, and methods without departing from the scope ofaspects of the disclosure, it is intended that all matter contained inthe above description and shown in the accompanying drawings shall beinterpreted as illustrative and not in a limiting sense.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) can be used in combination witheach other. In addition, many modifications can be made to adapt aparticular situation or material to the teachings of the variousembodiments of the disclosure without departing from their scope. Whilethe dimensions and types of materials described herein are intended todefine the parameters of the various embodiments of the disclosure, theembodiments are by no means limiting and are example embodiments. Manyother embodiments will be apparent to those of ordinary skill in the artupon reviewing the above description. The scope of the variousembodiments of the disclosure should, therefore, be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled. In the appended claims,the terms “including” and “in which” are used as the plain-Englishequivalents of the respective terms “comprising” and “wherein.”Moreover, the terms “first,” “second,” and “third,” etc. are used merelyas labels, and are not intended to impose numerical requirements ontheir objects. Further, the limitations of the following claims are notwritten in means-plus-function format and are not intended to beinterpreted based on 35 U.S.C. § 112(f), unless and until such claimlimitations expressly use the phrase “means for” followed by a statementof function void of further structure.

This written description uses examples to disclose the variousembodiments of the disclosure, including the best mode, and also toenable any person of ordinary skill in the art to practice the variousembodiments of the disclosure, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe various embodiments of the disclosure is defined by the claims, andcan include other examples that occur to those persons of ordinary skillin the art. Such other examples are intended to be within the scope ofthe claims if the examples have structural elements that do not differfrom the literal language of the claims, or if the examples includeequivalent structural elements with insubstantial differences from theliteral language of the claims.

The invention claimed is:
 1. An assembly for a transverseelectromagnetic (TEM) system, the assembly comprising: a support framecomprising an upper plate and a lower plate the upper plate defining afirst inner surface and an opposed first outer surface, the first innersurface oriented toward a TEM test space, the lower plate defining asecond inner surface and an opposed second outer surface, the secondinner surface oriented toward the first inner surface of the upper plateand toward the TEM test space, the TEM test space defined between thefirst inner surface of the upper plate and the second inner surface ofthe lower plate; at least one resistive sheet coupled to at least one ofthe upper plate or the lower plate the at least one resistive sheetextending parallel to the upper plate and lower plate from a peripheryof the support frame, wherein the resistive sheet has an inner enddisposed proximate the at least one of the upper plate or lower plateand an outer end disposed opposite the inner end, wherein the resistivesheet has a variable resistance that is greater at the outer end than atthe inner end.
 2. The assembly of claim 1, wherein the at least oneresistive sheet includes an upper resistive sheet coupled to the upperplate, and a lower resistive sheet coupled to the lower plate.
 3. Theassembly of claim 2, further comprising a plurality of lower blockportions disposed around an exterior of the support frame; a pluralityof upper block portions disposed above the plurality of lower blockportions; and a plurality of intermediate block portions interposedbetween the plurality of lower block portions and upper block portions;wherein the upper resistive sheet is interposed between the plurality ofupper block portions and the plurality of intermediate block portions,and the lower resistive sheet is interposed between the plurality oflower block portions and the plurality of intermediate block portions.4. The assembly of claim 1, wherein the resistive sheet includes a gridof resistive portions configured to provide the variable resistance. 5.The assembly of claim 1, wherein the at least one resistive sheet has aresistive side and a substrate side, the resistive side oriented awayfrom the at least one of the upper plate or lower plate the substrateside oriented toward the at least one of the upper plate or lower plate.6. The assembly of claim 5, wherein the at least one resistive sheet iscoupled to the at least one of the upper plate or lower plate withconductive tape.
 7. The assembly of claim 1, wherein the support framedefines a length extending from a source side toward an object side andwidth extending normal to the length, the assembly further comprisingresistive blocks disposed along the width proximate the object side,each resistive block having first and second resistive sides opposed toeach other and oriented along the width.
 8. The assembly of claim 7,wherein the resistive sides have a front end and a rear end, the frontend closer to the source side than the rear end, wherein the resistivesides have a variable resistance that is greater at the rear end than atthe front end.
 9. The assembly of claim 8, wherein the first resistiveside includes a first tapered resistive member tapered toward a bottomof the corresponding resistive block, and the second resistive sideincludes a second tapered resistive member tapered toward a top of thecorresponding resistive block.
 10. The assembly of claim 7, furthercomprising at least one intermediate block interposed between resistiveblocks.
 11. An assembly for a transverse electromagnetic (TEM) system,the assembly comprising: a support frame comprising an upper plate and alower plate the upper plate defining a first inner surface and anopposed first outer surface, the first inner surface oriented toward aTEM test space, the lower plate defining a second inner surface and anopposed second outer surface, the second inner surface oriented towardthe first inner surface of the upper plate and toward the TEM testspace, the TEM test space defined between the first inner surface of theupper plate and the second inner surface of the lower plate wherein thesupport frame defines a length extending from a source side toward anobject side and width extending normal to the length; and resistiveblocks disposed along the width proximate the object side, eachresistive block having first and second resistive sides opposed to eachother and oriented along the width.
 12. The assembly of claim 11,wherein the resistive sides have a front end and a rear end, the frontend closer to the source side than the rear end, wherein the resistivesides have a variable resistance that is greater at the rear end than atthe front end.
 13. The assembly of claim 12, wherein the first resistiveside includes a first tapered resistive member tapered toward a bottomof the corresponding resistive block, and the second resistive sideincludes a second tapered resistive member tapered toward a top of thecorresponding resistive block.
 14. The assembly of claim 11, furthercomprising at least one intermediate block interposed between resistiveblocks.
 15. A method comprising: providing a support frame comprising anupper plate and a lower plate the upper plate defining a first innersurface and an opposed first outer surface, the first inner surfaceoriented toward a transverse electromagnetic (TEM) test space, the lowerplate defining a second inner surface and an opposed second outersurface, the second inner surface oriented toward the first innersurface of the upper plate and toward the TEM test space, the TEM testspace defined between the first inner surface of the upper plate and thesecond inner surface of the lower plate; coupling at least one resistivesheet to at least one of the upper plate or the lower plate the at leastone resistive sheet extending parallel to the upper plate and lowerplate from an exterior of the support frame, wherein the resistive sheethas an inner end disposed proximate the at least one of the upper plateor lower plate and an outer end disposed opposite the inner end, whereinthe resistive sheet has a variable resistance that is greater at theouter end than at the inner end.
 16. The method of claim 15, furthercomprising coupling an upper resistive sheet to the upper plate, andcoupling a lower resistive sheet to the lower plate.
 17. The method ofclaim 15, further comprising providing a resistive grid of resistiveportions on the resistive sheet configured to provide the variableresistance.
 18. The method of claim 15, further comprising providing theat least one resistive sheet with a resistive side and a substrate side,orienting the resistive side away from the at least one of the upperplate or lower plate and orienting the substrate side toward the atleast one of the upper plate or lower plate.
 19. The method of claim 18,further comprising coupling the at least one resistive sheet to the atleast one of the upper plate or lower plate with conductive tape. 20.The method of claim 15, wherein the support frame defines a lengthextending from a source side toward an object side and width extendingnormal to the length, the method further comprising disposing resistiveblocks along the width proximate the object side, each resistive blockhaving first and second resistive sides opposed to each other andoriented along the width.